Facilitator Questions

1. Zygotic transcription begins at the mid blastula transition (MBT). What mechanisms can you imagine that prevent transcription before cycle 14? At what rate are genes transcribed? How long is interphase in pre-cycle 14 embryos?  How could you test the idea that the physical length of a gene determines when it is transcribed?
   
   
2. The first genes to be expressed at the onset of zygotic transcription at the mid blastula transition (MBT) are a group of genes called gap genes which includes hunchback and krueppel. These genes are expressed in relatively broad domains. Subsequently, the pair-rule genes (e.g. paired, runt, even-skipped) are expressed in stripes that are 4 cells wide. How is this pattern achieved? How is the pattern refined or, in other words, how does the broad expression pattern of the gap genes give rise to the expression pattern of the pair-rule genes? What does combinatorial signalling mean? Is the time at which the pair-rule genes are expressed important? What events or cell behaviours are regulated by the pair-rule genes?
   
   

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